This invention relates generally as indicated to an intra-circulatory monitoring system and method and a flush system therefor.
In the care of critically ill patients, a system known as intra-arterial monitoring has been developed for gathering accurate and reliable data for use in the diagnostic treatment and care of such patients. This technique is used for example, for obtaining patient blood pressure on a continuous basis. Such technique involves direct and continuous measurement of the blood pressure and is more accurate than indirect measurements obtained with an occlusive cuff. Cuff pressure values can be distorted by a variety of factors such as incorrectly applied cuffs or ill-fitting cuffs, or by pressures so low that sounds are lost.
Such intra-arterial monitoring systems involve the use of an indwelling catheter, a pressure transducer, a tubing and coupling system, and an electronic device for calculating and displaying patient blood pressure values on a continuous basis. This technique is now routinely used in operating rooms, intensive care units, and other areas of a hospital devoted to critical patient care and may be employed substantially anywhere in the circulatory system.
A primary component of the system is the monitoring device which, in the case of blood pressure observation, is a pressure transducer. This device is employed as a converter to change pressure from the blood within the artery to a proportional electronic signal. The pressure wave forms sensed by the transducer are displayed as analog signals on a cathode ray tube for visual study. Digital values such as the peak or systolic pressure and trough or diastolic pressure are calculated and displayed directly in digital form. This information is normally updated on a continuous basis to indicate or approximate real time values.
Such systems may also be used to take frequent blood specimens eliminating the need for frequent venipunctures. The system may also be used to facilitate the control or application of fluids within the blood such as heparin or protamine used before, during and following critical surgical procedures such as open heart surgery.
While the system has become commonplace in the treatment of critically ill patients, it is nonetheless of great importance that the display data be accurate, dependable and repeatable. As with any complex system, there are disadvantages which may develop which may compromise the system if they are not recognized and controlled. Some of the more frequent disadvantages in such systems are the contamination of the tubing system and the clinical use of any inaccurate data resulting from a system malfunction such as a transducer gain mismatch, improper zeroing, calibration, etc. Furthermore, as with other sensitive monitoring systems, signal damping and system noise are preferably minimized.
In the case of contamination, foreign substances introduced into the fluid system may result in inaccurate data. Typical examples are air bubbles and blood clots present in the fluid stream. A common form of such contamination which may result in distortion of the data obtained is the formation of air bubbles in the usually dome-shape pressure chamber to which the transducer is connected. These air bubbles or pockets generally accumulate from the atomizing effects of a solution under pressure passing through small orifices or may be remnants of poor set up and the initial flushing of the monitoring system.
Reference may be had to an article entitled "Intra-arterial Monitoring, Rescinding the Risks" of JoAnn Lamb, which appeared in the November, 1977 issue of Nursing '77 for a general description of such monitoring systems and some of the problems involved. A typical intra-arterial monitoring system comprises an indwelling arterial catheter which is inserted in an artery of the patient. The catheter is connected through a dynamic fluid line to a source of heparin enriched saline solution pressurized to approximately 300 mm Hg. Positioned within such line is a flush valve which includes a micropassage or restricted orifice through which solution passes into the catheter. The flush valve also includes a bypass passage so that the micropassage may be bypassed when desired. The system usually includes a static or dead end line positioned downstream of the micropassage which leads to a domed pressure chamber to which the transducer is connected. The transducer is, of course, connected to the electronic monitoring equipment. The transducer dome is transparent and is normally provided with a stopcock for manual venting.
The pressure of the saline solution is normally above the arterial pressure and assures a flow of the solution into the artery when needed. Heparin is normally employed to dissolve and discourage blood clots which might accumulate anyplace in the monitoring system, particularly in the indwelling catheter site.
The flush valve contains a metering orifice or passage that permits a constant controlled microflow of the heparin solution into the artery thus keeping the system free of clots and enhancing the accuracy of the fluid pressure generated electronic signals. The primary fluid flow line of the pressurized solution to the artery is intended to be a dynamic flowing line.
It is standard technique to clear this primary flow line occasionally of accumulated air or clots not handled by the microflow. It is also routine practice to withdraw arterial blood specimens through this line. Such withdrawal results in blood being aspirated up into the monitoring line. It therefore becomes necessary periodically to fast flush the blood, clots and air out of the primary dynamic line implementing the more rapid flow of the flush solution for a short period of time. This is normally accomplished by a manual actuation of the flush valve which momentarily bypasses the micropassage within the valve and such action then produces a more rapid flow condition in the primary line from the pressurized solution to the indwelling catheter.
Conventionally, the static line or passage connects from the flush valve downstream of the micropassage to a dome chamber which contains an isolation membrane to confine the fluid. The transducer and dome are assembled such that the membrane is in intimate contact with the transducer diaphragm thus sensing pressure on the membrane. The membrane permits the changing of transducers which are normally quite expensive and not disposable without compromising the sterility of the monitoring system. Accordingly, the static fluid branch to the transducer chamber and membrane is a stagnant line under normal monitoring and fast flush procedures.
In such systems, the dome or chamber is usually provided with a stopcock which may be opened to purge air or unwanted fluids from the dome to air or ambient atmosphere. The venting of air and/or fluids from the transducer chamber or dome by the stopcock method is at best a messy situation. Fluids within the dome can and do run over the transducer and dome making removal and separation difficult. Moreover, the patient may be draped for surgery and such venting may contaminate the sterile environment. Opening of the stopcock may require the use of both hands and must be done initially when the system is first set up and flushed, and then every time air or blood accumulates within the chamber.